Thermoplastic holographic media

ABSTRACT

The present invention provides an article comprising: a binder component, a polymerizable component; and a photoinitiator component comprising at least one photoinitiator that causes the polymerizable component to form a polymer or co-polymer when a portion of the polymerizable component is exposed to a light source. The present invention also provides a method for making such an article, and a method and a system for holographically recording a spatial light distribution to such an article. The present invention also provides an article comprising: a binder component and a photoactive component, a method of making such an article, a method of recording to such an article and a system for recording to such an article.

BACKGROUND

1. Field of the Invention

The present invention relates to optical articles including holographicrecording media, in particular media useful either with holographicstorage systems or as components such as optical filters or beamsteerers.

2. Related Art

Developers of information storage devices and methods continue to seekincreased storage capacity. As part of this development, so-calledpage-wise memory systems, in particular holographic systems, have beensuggested as alternatives to conventional memory devices. Page-wisesystems involve the storage and readout of an entire two-dimensionalrepresentation, e.g., a page, of data. Typically, recording light passesthrough a two-dimensional array of dark and transparent areasrepresenting data, and the holographic system stores, in threedimensions, holographic representations of the pages as patterns ofvarying refractive index imprinted into a storage medium. Holographicsystems are discussed generally in D. Psaltis et al., “HolographicMemories,” Scientific American, November 1995, the disclosure of whichis hereby incorporated by reference. One method of holographic storageis phase correlation multiplex holography, which is described in U.S.Pat. No. 5,719,691, issued Feb. 17, 1998, the disclosure of which ishereby incorporated by reference. In one embodiment of phase correlationmultiplex holography, a reference light beam is passed through a phasemask, and intersected in the recording medium with a signal beam thathas passed through an array representing data, thereby forming ahologram in the medium. The spatial relation of the phase mask and thereference beam is adjusted for each successive page of data, therebymodulating the phase of the reference beam and allowing the data to bestored at overlapping areas in the medium. The data is laterreconstructed by passing a reference beam through the original storagelocation with the same phase modulation used during data storage. It isalso possible to use volume holograms as passive optical components tocontrol or modify light directed at the medium, e.g., filters or beamsteerers. Writing processes that provide refractive index changes arealso capable of forming articles such as waveguides.

The capabilities of typical holographic storage systems are limited inpart by the storage media. Iron-doped lithium niobate has been used as astorage medium for research purposes for many years. However, lithiumniobate is expensive, exhibits poor sensitivity (1 J/cm²), has low indexcontrast (Δn of about 10⁻⁴), and exhibits destructive read-out (i.e.,images are destroyed upon reading). Alternatives have therefore beensought, particularly in the area of photosensitive polymer films. See,e.g., W. K. Smothers et al., “Photopolymers for Holography,” SPIEOE/Laser Conference, 1212-03, Los Angeles, Calif., 1990, the disclosureof which is hereby incorporated by reference. The material described inthis article contains a photoimageable system containing a liquidmonomer material (the photoactive monomer) and a photoinitiator (whichpromotes the polymerization of the monomer upon exposure to light),where the photoimageable system is in an organic polymer host matrixthat is substantially inert to the exposure light. During writing ofinformation into the material (by passing recording light through anarray representing data), the monomer polymerizes in the exposedregions. Due to the lowering of the monomer concentration caused by thepolymerization, monomer from the dark, unexposed regions of the materialdiffuses to the exposed regions. The polymerization and resultingconcentration gradient create a refractive index change, forming thehologram representing the data. Unfortunately, deposition onto asubstrate of the pre-formed matrix material containing thephotoimageable system requires use of solvent and the necessity of usinga solvent deposition process for forming the holographic storage medium.For example, it is difficult to use a solvent-based deposition method toform a data storage media having thicknesses greater than 150 μm, or toform a holographic recording medium that does not include a substrateonto which the holographic recording medium is deposited. Also, only alimited number of types of plastic may be used in an article formedusing a solvent-based deposition method, and only a limited amount ofpost-processing may be performed on an article formed using asolvent-based deposition method.

SUMMARY

According to a first broad aspect of the present invention, there isprovided an article comprising: a binder component comprising at leastone thermoplastic; a polymerizable component comprising at least onephotoactive monomer that is soluble in the binder component; and aphotoinitiator component comprising at least one photoinitiator thatcauses the polymerizable component to form a polymer or co-polymer whena portion of the polymerizable component is exposed to a light source,wherein the article is capable of recording spatial light distributionvia a spatial refractive index change.

According to a second broad aspect of the invention, there is provided amethod for making a solid article comprising the following steps: (a)mixing together a binder component, a polymerizable component and aphotoinitiator component to form a mixture; (b) heating the mixture toform a substantially homogeneous liquid; and (c) cooling the liquid toform the solid article, wherein the binder component comprises at leastone thermoplastic, wherein the polymerizable component comprises atleast one photoactive monomer that is soluble in the binder component,wherein the photoinitiator component comprises at least onephotoinitiator that causes the polymerizable component to form a polymeror co-polymer when a portion of the polymerizable component is exposedto a light source, and wherein the article is capable of recordingspatial light distribution via a spatial refractive index change.

According to a third broad aspect of the invention, there is provided amethod for holographically recording a spatial light distribution via aspatial refractive index change to a holographic recording mediumcomprising: providing the holographic recording medium; and formingholographic gratings in the holographic recording medium byholographically recording the spatial light distribution via the spatialrefractive index change to the holographic recording medium, wherein theholographic recording medium comprises: a binder component comprising atleast one thermoplastic; a polymerizable component comprising at leastone photoactive monomer that is soluble in the binder component; and aphotoinitiator component comprising at least one photoinitiator thatcauses the polymerizable component to form a polymer or co-polymer whena portion of the polymerizable component is exposed to a light source.

According to a fourth broad aspect of the invention, there is provided asystem for holographically recording a spatial light distribution via aspatial refractive index change to a holographic recording mediumcomprising: the holographic recording medium; and means for formingholographic gratings in the holographic recording medium by recordingthe spatial light distribution via the spatial refractive index changeto the holographic recording medium, wherein the holographic recordingmedium comprises: a binder component comprising at least onethermoplastic; a polymerizable component comprising at least onephotoactive monomer that is soluble in the binder component; and aphotoinitiator component comprising at least one photoinitiator thatcauses the polymerizable component to form a polymer or co-polymer whena portion of the polymerizable component is exposed to a light source.

According to a fifth broad aspect of the invention, there is provided asolid article comprising: a binder component comprising at least onethermoplastic; and a photoactive component comprising at least onephotoactive molecule, wherein the article is capable of recordingspatial light distribution via a spatial refractive index.

According to a sixth broad aspect of the invention, there is provided amethod for making a solid article comprising the following steps: (a)mixing a binder component with a photoactive component; (b) heating themixture to form a substantially homogeneous liquid; and (c) cooling theliquid to form the solid article, wherein the binder component comprisesat least one thermoplastic, wherein the photoactive component comprisesat least one photoactive molecule, and wherein the solid article iscapable of recording spatial light distribution via a spatial refractiveindex change.

According to a seventh broad aspect of the invention, there is provideda method for holographically recording a spatial light distribution viaa spatial refractive index change to a holographic recording mediumcomprising the following steps: (a) providing the holographic recordingmedium; and (b) forming holographic gratings in the holographicrecording medium by holographically recording the spatial lightdistribution via the spatial refractive index change to the holographicrecording medium, wherein the holographic recording medium comprises: abinder component comprising at least one thermoplastic; and aphotoactive component comprising at least one photoactive molecule.

According to an eighth broad aspect of the invention, there is provideda system for holographically recording a spatial light distribution viaa spatial refractive index change to a holographic recording mediumcomprising: (a) the holographic recording medium; and (b) means forforming holographic gratings in the holographic recording medium byrecording the spatial light distribution via the spatial refractiveindex change to the holographic recording medium, wherein theholographic recording medium comprises: a binder component comprising atleast one thermoplastic; and a photoactive component comprising at leastone photoactive molecule.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described in conjunction with the accompanyingdrawings, in which:

The sole drawing FIGURE shows a basic holographic storage systemaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

It is advantageous to define several terms before describing theinvention. It should be appreciated that the following definitions areused throughout this application.

DEFINITIONS

Where the definition of terms departs from the commonly used meaning ofthe term, applicant intends to utilize the definitions provided below,unless specifically indicated.

For the purposes of the present invention, the term “light source”refers to any source of electromagnetic radiation of any wavelength. Inone embodiment, the light source of the present invention is a laser ofa particular wavelength.

For the purposes of the present invention, the term “capable of beingused as a holographic storage medium” refers to an article that iscapable of storing, in three dimensions, holographic representations ofone or more pages as patterns of varying refractive index imprinted intoan article of the present invention.

For the purposes of the present invention, the term “data page” or“page” refers to the conventional meaning of data page as used withrespect to holography. For example, a data page may be a page of data,one or more pictures, etc. to be recorded to a holographic storagemedium, such as an article of the present invention.

For the purposes of the present invention, the term “recording data”refers to storing holographic representations of one or more pages aspatterns of varying refractive index in an article of the presentinvention.

For the purposes of the present invention, the term “reading data”refers to retrieving data stored as holographic representations from anarticle of the present invention.

For the purposes of the present invention, the term “binder component”refers to one or more thermoplastic materials of the present invention.Generally there is a sufficient amount of thermoplastic material in thebinder component of an article of the present invention to allow anarticle of the present invention to be solid at room temperature andbehave as a thermoplastic. Although the amount of thermoplastic materialin an article of the present invention may vary, in one embodiment ofthe present invention, the amount of thermoplastic material may be aslow as 5 wt % of an article of the present invention.

For the purposes of the present invention, the term “different form”refers to an article of the present invention being processed to form aproduct having a different form such as processing an article comprisinga block of material, powder of material, chips of material, etc. into amolded product, a sheet, a free flexible film, a stiff card, a flexiblecard, an extruded product, a film deposited on a substrate, etc.

For the purposes of the present invention, the term “particle material”refers to a material that is made by grinding, shredding, fragmenting orotherwise subdividing an article into smaller components or to amaterial that is comprised of small components such as a powder.

For the purposes of the present invention, the term “free flexible film”refers to a thin sheet of flexible material that maintains its formwithout being supported on a substrate. Examples of free flexible filmsinclude the various types of plastic wraps used in food storage.

For the purposes of the present invention, the term “stiff article”refers to an article that may crack or crease when bent. An example of astiff article is a plastic credit card, a DVD, a transparency, wrappingpaper, a shipping box, etc.

For the purposes of the present invention, the term “volatile compound”refers to any chemical with a high vapor pressure and/or a boiling pointbelow 150° C. Examples of volatile compounds include: acetone, methylenechloride, toluene, etc. An article, mixture or component is “volatilecompound free” if the article, mixture or component does not include avolatile compound.

For the purposes of the present invention, the term “oligomer” refers toa polymer having approximately 30 repeat units or less or any largemolecule able to diffuse at least 100 nm in approximately 2 minutes atroom temperature when dissolved in the article of the present invention.Such oligomers may contain one or more polymerizable groups whereby thepolymerizable groups may be the same or different from other possiblemonomers in the polymerizable component. Furthermore, when more than onepolymerizable group is present on the oligomer, they may be the same ordifferent. Additionally, oligomers may be dendritic.

For the purpose of the present invention, the term “photoinitiator”refers to the conventional meaning of the term photoinitiator and alsorefers to sensitizers and dyes. In general, a photoinitiator causes thecuring of a material, such as a photoactive monomer, when the materialcontaining the photoinitiator is exposed to light of a wavelength thatactivates the photoinitiator. The photoinitiator may refer to acombination of components, some of which individually are not lightsensitive, yet in combination are capable of curing the photoactivemonomer; examples are dye/amine, sensitizer/iodonium salt, dye/boratesalt, etc.

For the purposes of the present invention, the term “photoinitiatorcomponent” refers to a single photoinitiator or a combination of two ormore photoinitiators. For example, two or more photoinitiators may beused in the photoinitiator component of the present invention to allowrecording at two or more different wavelengths of light.

For the purposes of the present invention the term “polymerizablecomponent” refers to a mixture of one or more photoactive monomers, andpossibly one or more additional monomers or oligomers that are capableof forming a polymer.

For the purposes of the present invention, the term “photobinding”refers to the forming of a covalent or noncovalent bond between anactivated photoactive molecule and a photobinding receptor uponirradiation with an appropriate light source.

For the purposes of the present invention, the term “photoactivemolecule” refers to any molecule that upon irradiation with anappropriate light source becomes active toward bonding with aphotobinding receptor. A given photoactive molecule may be as large asan oligomer as defined previously; additionally, it may include morethan one functional group, and each functional group may be the same ordifferent. A given photoactive molecule may also contain photobindingreceptors.

For the purposes of the present invention, the term “photobindingreceptor” refers to a functional group that reacts with an activatedphotoactive molecule. The photobinding receptor may either be the sameor different functionality from the photoactive molecule. In oneembodiment of the present invention, the photobinding receptor ispresent on one or more binders and/or one or more oligomers of acomposition used to make an article of the present invention.

For the purposes of the present invention, the term “photoactivecomponent” refers to a single photoactive molecule or a mixture ofphotoactive molecules.

For the purposes of the present invention, the term “photoactivemonomer” refers to the general meaning of the term “photoactivemonomer,” i.e., a monomer that polymerizes in the presence of aphotoinitiator that has been activated by being exposed to a lightsource. In reference to the functional group that undergoes curing, thephotoactive monomer comprises at least one such functional group. It isalso understood that there exist photoactive monomers that are alsophotoinitiators, such as N-methylmaleimide, derivatized acetophenones,etc. In such a case, it is understood that the photoactive monomer ofthe present invention may also be a photoinitiator.

For purposes of the present invention, the term “photopolymer” refers toa polymer formed by one or more photoactive monomers, and possibly oneor more additional monomers or oligomers.

For the purposes of the present invention, the term “plasticizer” refersto the conventional meaning of the term plasticizer. In general, aplasticizer is a compound added to a polymer both to facilitateprocessing and to increase the flexibility and/or toughness of a productby internal modification (salvation) of a polymer molecule.

For the purposes of the present invention, the term “thermoplastic”refers to the conventional meaning of thermoplastic, i.e., a compoundsubstance that exhibits the property of a material, such as a highpolymer, that softens when exposed to heat and generally returns to itsoriginal condition when cooled to room temperature. Examples ofthermoplastics include, but are not limited to: poly(methyl vinylether-alt-maleic anhydride), poly(vinyl acetate), poly(styrene),poly(propylene), poly(ethylene oxide), linear nylons, linear polyesters,linear polycarbonates, linear polyurethanes, etc.

For the purposes of the present invention, the term “room temperaturethermoplastic” refers to a thermoplastic that is solid at roomtemperature, i.e., will not cold flow at room temperature.

For the purposes of the present invention, the term “room temperature”refers to the commonly accepted meaning of room temperature.

For the purposes of the present invention, the term “slow thermosettingagent” refers to a compound added to an article of the present inventionthat will cause one or more thermoplastics in the binder component ofthe article to eventually thermoset, but which does not cause any of thethermoplastics in the binder component to become thermoset in fewer than10 minutes when the article is cooled back to room temperature after thearticle has been heated to be in a flowable state.

For the purpose of this invention, the term “photoreversible” refers tomaterials such as photoactive molecules that are photoreversible, suchas photochromics, photorefractives, and photodimerizations (2+2 or 4+4).However, in many embodiments of the present invention, mass diffusionmay be the main cause of grating formation. For instance, when using anazo compound in a photoreversible isomerization, it is known that thetwo different possible isomers have different solubilities. Thus, in themass diffusion scenario, light may be used to change the solubility of afreely diffusing component, thus creating regions where the solubilityof the freely diffusing component is based on the spatial lightdistribution. Additionally, photodimerization can naturally incorporatemass diffusion, as one of the photoactive molecules in the photoactivecomponent may be freely diffusing until it dimerizes with a photobindingreceptor that is attached to the binder component.

DESCRIPTION

Previous holographic recording media have been a crosslinked matrix, aliquid, or solvent cast before recording of a hologram in the media. Incontrast, the medium of the present invention is a meltable-solidarticle at room temperature. The medium of the present invention behavesas a thermoplastic material with a melting temperature above roomtemperature.

The drawing FIGURE illustrates the basic components of a holographicsystem 10. System 10 contains a modulating device 12, a photorecordingmedium 14, and a sensor 16. Modulating device 12 is any device capableof optically representing data in two-dimensions. Device 12 is typicallya spatial light modulator that is attached to an encoding unit thatencodes data onto the modulator. Based on the encoding, device 12selectively passes or blocks portions of a signal beam 20 passingthrough device 12. In this manner, beam 20 is encoded with a data image.The image is stored by interfering the encoded signal beam 20 with areference beam 22 at a location on or within photorecording medium 14.The interference creates an interference pattern (or hologram) that iscaptured within medium 14 as a pattern of, for example, varyingrefractive index. It is possible for more than one holographic image tobe stored at a single location, or for holograms to be stored inoverlapping positions, by, for example, varying the angle, thewavelength, or the phase of the reference beam 22, depending on theparticular reference beam employed. Signal beam 20 typically passesthrough lens 30 before being intersected with reference beam 22 inmedium 14. It is possible for reference beam 22 to pass through lens 32before this intersection. Once data is stored in medium 14, it ispossible to retrieve the data by intersecting reference beam 22 withmedium 14 at the same location and at the same angle, wavelength, orphase at which reference beam 22 was directed during storage of thedata. The reconstructed data passes through lens 34 and is detected bysensor 16. Sensor 16 is, for example, a charge coupled device or anactive pixel sensor. Sensor 16 typically is attached to a unit thatdecodes the data.

In one embodiment of the present invention, the article of the presentinvention is formed by steps including: mixing a binder component, apolymerizable component, and photoinitiator component to form a mixture;heating the mixture to form a homogeneous liquid mixture; and coolingthe liquid mixture in such a manner as to form an optically flatarticle. In one embodiment the difference in surface topography is nomore than λ/2. The thermoplastics in the binder component and monomersand oligomers in the polymerizable component are selected such that (a)the process of heating the mixture of components to make the resultingarticle homogeneous does not trigger the reaction by which thephotoactive monomer will be polymerized during writing of a pattern,e.g., data, and (b) the thermoplastics in the binder component and thephotopolymer resulting from polymerization of the photoactive monomer,mixture of monomers, or the mixture of one or more monomers and one ormore oligomers in the polymerizable component, are compatible with eachother.

In one embodiment of the present invention, the article of the presentinvention exhibits an elastic modulus of at least about 10⁵ Pa,generally about 10⁵ Pa to about 10⁹ Pa, and advantageously about 10⁶ Pato about 10⁸ Pa.

The compatibility of the binder component and the photopolymer of thepresent invention tend to prevent large-scale (preferably not >100 nm)phase separation of the binder component and the photopolymer, suchlarge-scale phase separation typically leading to undesirable hazinessor opacity. In one embodiment, the photoactive monomer andthermoplastics in the binder component are substantially free ofcross-reaction during the process of article formation, and thephotoactive monomer remains substantially inert. In addition, due to thephotoactive monomer remaining inert during the process of making thearticle optically flat, there is no interference of the subsequentpolymerization of the photoactive monomer.

In one embodiment of the present invention, at least one photoactivemonomer in the polymerizable component contains one or more moieties,excluding the monomer functional groups, that are substantially absentfrom the binder component. Substantially absent means that less than 20mole percent (based on the repeat unit of the thermoplastics in thebinders) of the binder component would contain the particular moiety.The resulting optical article is capable of exhibiting desirablerefractive index contrast due to the independence of the bindercomponent from the photoactive monomer.

As discussed above, formation of a hologram, waveguide, or other opticalarticle relies on a refractive index contrast (Δn) between exposed andunexposed regions of a medium, this contrast being at least partly dueto monomer diffusion to exposed regions. High index contrast isgenerally desired because it provides improved signal strength whenreading a hologram, and provides efficient confinement of an opticalwave in a waveguide. One way to provide high index contrast in theinvention is to use a photoactive monomer having moieties (referred toas index-contrasting moieties) that are substantially absent from thebinder component, and that exhibit a refractive index substantiallydifferent from the index exhibited by the bulk of the binder component.For example, high contrast may be obtained by using a binder componentthat contains primarily aliphatic or saturated alicyclic moieties with alow concentration of heavy atoms and conjugated double bonds (providinglow index) and a photoactive monomer made up primarily of aromatic orsimilar high-index moieties.

In applications of the present invention needing low scatter such ashigh density data storage, polymers are considered to be compatible if ablend of the polymers is characterized, in 90° light scattering, by aRayleigh ratio (R90°) less than 7×10⁻³ cm⁻¹. The Rayleigh ratio, Rθ, isa conventionally known property, and is defined as the energy scatteredby a unit volume in the direction θ, per steradian, when a medium isilluminated with a unit intensity of unpolarized light, as discussed inM. Kerker, The Scattering of Light and Other Electromagnetic Radiation,Academic Press, San Diego, 1969, the disclosure of which is herebyincorporated by reference. The light source used for the measurement isgenerally a laser having a wavelength in the visible part of thespectrum. Normally, the wavelength intended for use in writing hologramsis used. The scattering measurements are made upon a photorecordingmaterial that has been flood exposed. The scattered light is collectedat an angle of 90° from the incident light, typically by aphotodetector. It is possible to place a narrowband filter, centered atthe laser wavelength, in front of such a photodetector to blockfluorescent light, although such a step is not required. The Rayleighratio is typically obtained by comparison to the energy scatter of areference material having a known Rayleigh ratio.

Polymer blends which are considered to be miscible, e.g., according toconventional tests such as exhibition of a single glass transitiontemperature, will typically be compatible as well, i.e., miscibility isa subset of compatibility. Standard miscibility guidelines and tablesare therefore useful in selecting a compatible blend. However, it ispossible for polymer blends that are immiscible to be compatibleaccording to the light scattering test above.

A polymer blend is generally considered to be miscible if the blendexhibits a single glass transition temperature, T_(g), as measured byconventional methods. An immiscible blend will typically exhibit twoglass transition temperatures corresponding to the T_(g) values of theindividual polymers. T_(g) testing is most commonly performed bydifferential scanning calorimetry (DSC), which shows the T_(g) as a stepchange in the heat flow (typically the ordinate). The reported T_(g) istypically the temperature at which the ordinate reaches the mid-pointbetween extrapolated baselines before and after the transition. It isalso possible to use Dynamic Mechanical Analysis (DMA) to measure T_(g).DMA measures the storage modulus of a material, which drops severalorders of magnitude in the glass transition region. It is possible incertain cases for the polymers of a blend to have individual T_(g)values that are close to each other. In such cases, conventional methodsfor resolving such overlapping T_(g) should be used, such as discussedin Brinke et al., “The thermal characterization of multi-componentsystems by enthalpy relaxation,” Thermochimica Acta., 238 (1994), at 75,the disclosure of which is hereby incorporated by reference.

Binder polymer and photopolymer that exhibit miscibility are capable ofbeing selected in several ways. For example, several publishedcompilations of miscible polymers are available, such as O. Olabisi etal., Polymer-Polymer Miscibility, Academic Press, New York, 1979; L. M.Robeson, MMI. Press Symp. Ser., 2, 177, 1982; L. A. Utracki, PolymerAlloys and Blends: Thermodynamics and Rheology, Hanser Publishers,Munich, 1989; and S. Krause in Polymer Handbook, J. Brandrup and E. H.Immergut, Eds.; 3rd Ed., Wiley Interscience, New York, 1989, pp. VI347-370, the disclosures of which are hereby incorporated by reference.Even if a particular polymer of interest is not found in suchreferences, the approach specified allows determination of a compatiblephotorecording material by employing a control sample.

Determination of miscible or compatible blends is further aided byintermolecular interaction considerations that typically drivemiscibility. For example, it is well known that polystyrene andpoly(methylvinylether) are miscible because of an attractive interactionbetween the methyl ether group and the phenyl ring. It is thereforepossible to promote miscibility, or at least compatibility, of twopolymers by using a methyl ether group in one polymer and a phenyl groupin the other polymer. It has also been demonstrated that immisciblepolymers are capable of being made miscible by the incorporation ofappropriate functional groups that can provide ionic interactions. (SeeZ. L. Zhou and A. Eisenberg, J. Polym. Sci., Polym. Phys. Ed., 21 (4),595, 1983; R. Murali and A. Eisenberg, J. Polym. Sci., Part B: Polym.Phys., 26 (7), 1385, 1988; and A. Natansohn et al., Makromol. Chem.,Macromol. Symp., 16, 175, 1988, the disclosures of which are herebyincorporated by reference.) For example, polyisoprene and polystyreneare immiscible. However, when polyisoprene is partially sulfonated (5%),and 4-vinyl pyridine is copolymerized with the polystyrene, the blend ofthese two functionalized polymers is miscible. It is contemplated thatthe ionic interaction between the sulfonated groups and the pyridinegroup (proton transfer) is the driving force that makes this blendmiscible. Similarly, polystyrene and poly(ethyl acrylate), which arenormally immiscible, have been made miscible by lightly sulfonating thepolystyrene. (See R. E. Taylor-Smith and R. A. Register, Macromolecules,26, 2802, 1993, the disclosure of which is hereby incorporated byreference.) Charge-transfer has also been used to make miscible polymersthat are otherwise immiscible. For example it has been demonstratedthat, although poly(methyl acrylate) and poly(methyl methacrylate) areimmiscible, blends in which the former is copolymerized with(N-ethylcarbazol-3-yl)methyl acrylate (electron donor) and the latter iscopolymerized with 2-[(3,5-dinitrobenzoyl)oxy]ethyl methacrylate(electron acceptor) are miscible, provided the right amounts of donorand acceptor are used. (See M. C. Piton and A. Natansohn,Macromolecules, 28, 15, 1995, the disclosure of which is herebyincorporated by reference.) Poly(methyl methacrylate) and polystyreneare also capable of being made miscible using the correspondingdonor-acceptor co-monomers (See M. C. Piton and A. Natansohn,Macromolecules, 28, 1605, 1995, the disclosure of which is herebyincorporated by reference).

A variety of test methods exist for evaluating the miscibility orcompatibility of polymers, as reflected in the recent overview publishedin A. Hale and H. Bair, Ch. 4-“Polymer Blends and Block Copolymers,”Thermal Characterization of Polymeric Materials, 2nd Ed., AcademicPress, 1997, the disclosure of which is hereby incorporated byreference. For example, in the realm of optical methods, opacitytypically indicates a two-phase material, whereas clarity generallyindicates a compatible system. Other methods for evaluating miscibilityinclude neutron scattering, infrared spectroscopy (IR), nuclear magneticresonance (NMR), x-ray scattering and diffraction, fluorescence,Brillouin scattering, melt titration, calorimetry, andchemilluminescence. See, for example, L. Robeson, supra; S. Krause,Chemtracts-Macromol. Chem., 2, 367, 1991a; D. Vesely in Polymer Blendsand Alloys, M. J. Folkes and P. S. Hope, Eds., Blackie Academic andProfessional, Glasgow, pp. 103-125; M. M. Coleman et al., SpecificInteractions and the Miscibility of Polymer Blends, TechnomicPublishing, Lancaster, Pa., 1991; A. Garton, Infrared Spectroscopy ofPolymer Blends Composites and Surfaces, Hanser, New York, 1992; L. W.Kelts et al., Macromolecules, 26, 2941, 1993; and J. L. White and P. A.Mirau, Macromolecules, 26, 3049, 1993; J. L. White and P. A. Mirau,Macromolecules, 27, 1648, 1994; and C. A. Cruz et al., Macromolecules,12, 726, 1979; and C. J. Landry et al., Macromolecules, 26, 35, 1993,the disclosures of which are hereby incorporated by reference.

Compatibility has also been promoted in otherwise incompatible polymersby incorporating reactive groups into the polymer matrix, where suchgroups are capable of reacting with the photoactive monomer during theholographic recording step. Some of the photoactive monomer will therebybe grafted onto the matrix during recording. If there are enough ofthese grafts, it is possible to prevent or reduce phase separationduring recording.

A holographic recording medium of the present invention is formed suchthat holographic writing and reading to the medium are possible.Typically, fabrication of the medium involves depositing bindercomponent/polymerizable component/photoinitiator component mixturebetween two plates using, for example, a gasket to contain the mixture.The plates are typically glass, but it is also possible to use othermaterials transparent to the radiation used to write data, e.g., aplastic such as polycarbonate or poly(methyl methacrylate). It ispossible to use spacers between the plates to maintain a desiredthickness for the recording medium. In applications requiring opticalflatness, the melted mixture may shrink during cooling and thus distortthe optical flatness of the article. To reduce such effects, it isuseful to place the article between plates in an apparatus containingmounts, e.g., vacuum chucks, capable of being adjusted in response tochanges in parallelism and/or spacing. In such an apparatus, it ispossible to monitor the parallelism in real-time by use of conventionalinterferometric methods, and to make any necessary adjustments to theheating/cooling process. Additionally, an article or substrate of thepresent invention may have an antireflective coating and/or be edgesealed to exclude water or oxygen. An antireflective coating may bedeposited on an article or substrate by various processes such aschemical vapor deposition and an article or substrate may be edge sealedusing known methods. The photorecording material of the presentinvention is also capable of being supported in other ways. Moreconventional polymer processing is also envisioned, e.g., closed moldformation or sheet extrusion. A stratified medium is also contemplated,i.e., a medium containing multiple substrates, e.g., glass, with layersof photorecording material disposed between the substrates.

Because the article of the present invention exhibits thermoplasticproperties, an article of the present invention may also be heated aboveits melting temperature and processed in the ways described above forthe binder component/polymerizable component/photoinitiator componentmixture.

A holographic recording medium of the present invention is then capableof being used in a holographic system such as discussed previously. Theamount of information capable of being stored in a holographic medium isproportional to the product of: the refractive index contrast, Δn, ofthe photorecording material, and the thickness, d, of the photorecordingmaterial. (The refractive index contrast, Δn, is conventionally known,and is defined as the amplitude of the sinusoidal variations in therefractive index of a material in which a plane-wave, volume hologramhas been written. The refractive index varies as: n(x)=n₀+Δn cos(K_(x)),where n(x) is the spatially varying refractive index, x is the positionvector, K is the grating wave vector, and n₀ is the baseline refractiveindex of the medium. See, e.g., P. Hariharan, Optical Holography:Principles, Techniques and Applications, Cambridge University Press,Cambridge, 1991, at 44, the disclosure of which is hereby incorporatedby reference.) The Δn of a material is typically calculated from thediffraction efficiency or efficiencies of a single volume hologram or amultiplexed set of volume holograms recorded in a medium. The Δn isassociated with a medium before writing, but is observed by measurementperformed after recording. Advantageously, the photorecording materialof the invention exhibits a Δn of 3×10⁻³ or higher.

Examples of other optical articles include beam filters, beam steerersor deflectors, and optical couplers. (See, e.g., L. Solymar and D.Cooke, Volume Holography and Volume Gratings, Academic Press, 315-327(1981), the disclosure of which is hereby incorporated by reference.) Abeam filter separates part of an incident laser beam that is travelingalong a particular angle from the rest of the beam. Specifically, theBragg selectivity of a thick transmission hologram is able toselectively diffract light along a particular angle of incidence, whilelight along other angles travels undeflected through the hologram. (See,e.g., J. E. Ludman et al., “Very thick holographic nonspatial filteringof laser beams,” Optical Engineering, Vol. 36, No. 6, 1700 (1997), thedisclosure of which is hereby incorporated by reference.) A beam steereris a hologram that deflects light incident at the Bragg angle. Anoptical coupler is typically a combination of beam deflectors that steerlight from a source to a target. These articles, typically referred toas holographic optical elements, are fabricated by imaging a particularoptical interference pattern within a recording medium, as discussedpreviously with respect to data storage. Media for these holographicoptical elements are capable of being formed by the techniques discussedherein for recording media or waveguides.

As mentioned previously, the materials principles discussed herein areapplicable not only to hologram formation, but also to formation ofoptical transmission devices such as waveguides. Polymeric opticalwaveguides are discussed for example in B. L. Booth, “OpticalInterconnection Polymers,” in Polymers for Lightwave and IntegratedOptics, Technology and Applications, L. A. Hornak, ed., Marcel Dekker,Inc. (1992); U.S. Pat. No. 5,292,620; and U.S. Pat. No. 5,219,710, thedisclosures of which are hereby incorporated by reference. Essentially,the recording material of the present invention is irradiated in adesired waveguide pattern to provide refractive index contrast betweenthe waveguide pattern and the surrounding (cladding) material. It ispossible for exposure to be performed, for example, by a focused laserlight or by use of a mask with a non-focused light source. Generally, asingle layer is exposed in this manner to provide the waveguide pattern,and additional layers are added to complete the cladding, therebycompleting the waveguide. This process is discussed for example at pages235-36 of Booth, supra, and Cols. 5 and 6 of U.S. Pat. No. 5,292,620,the disclosure of which is hereby incorporated by reference. A benefitof the present invention is that by using conventional moldingtechniques, it is possible to mold the binder mixture into a variety ofshapes prior to formation of the article by cooling to room temperature.For example, the binder mixture can be molded into ridge waveguides,wherein refractive index patterns are then written into the moldedstructures. It is thereby possible to easily form structures such asBragg gratings. This feature of the present invention increases thebreadth of applications in which such polymeric waveguides would beuseful. An article of the present invention may be used as a holographicrecording medium that departs from prior data storage media by employinga binder made of one or more thermoplastic polymers in which themonomers and oligomers that form the grating are dissolved. The articleof the present invention includes a binder component including one ormore thermoplastics, a polymerizable component including one or morephotoactive monomers and possibly one or more oligomers, and aphotoinitiator component including one or more photoinitiators.

The binder component allows an article of the present invention tobehave as if the entire article was a thermoplastic. That is, the bindercomponent allows the article to be processed similar to the way that athermoplastic is processed, i.e., molded into a shaped article, blowninto a film, deposited in liquid form on a substrate, extruded, rolled,pressed, made into a sheet of material, etc. and then allowed to hardenat room temperature to take on a stable shape or form. The bindercomponent may comprise one or more thermoplastics. Suitablethermoplastics include poly(methyl vinyl ether-alt-maleic anhydride),poly(vinyl acetate), poly(styrene), poly(propylene), poly(ethyleneoxide), linear nylons, linear polyesters, linear polycarbonates, linearpolyurethanes, poly(vinyl chloride), poly(vinyl alcohol-co-vinylacetate). The amount of thermoplastic used in the holographic recordingmedium of the present invention is preferably enough that the entireholographic recording medium effectively acts as a thermoplastic formost processing purposes. The binder component of the holographicrecording medium may make up as much as 5%, preferably as much as 50%,and more preferably as much as 90% of the holographic recording mediumby weight. The amount of any given binder in the holographic recordingmedium may vary based on clarity, refractive index, melting temperature,T_(g), color, birefringence, solubility, etc. of the thermoplastic orthermoplastics that make up the binder component. Additionally, theamount of binder component in the holographic recording medium may varybased on the article's final form, whether it is a solid, a flexiblefilm, or an adhesive.

In one embodiment, the binder may include a telechelic thermoplasticresin—meaning that the thermoplastic polymer may be functionalized withreactive groups that covalently crosslink the thermoplastic in thebinder with the polymer formed from the polymerizable component duringgrating formation. Such crosslinking makes the gratings stored in theholographic recording medium very stable, even to elevated temperaturesfor extended periods of time.

In another embodiment of the present invention, the thermoplastic orthermoplastics in the binder become crosslinked noncovalently with thepolymer formed upon grating formation by using a functionalizedthermoplastic polymer in the binder component. Examples of suchnon-covalent bonding include ionic bonding, hydrogen bonding,dipole-dipole bonding, aromatic pi stacking, etc.

According to an embodiment of the present invention, the polymerizablecomponent of an article of the present invention includes one or moremonomers, at least one of which is a photoactive monomer, that formgratings made of a polymer or co-polymer when exposed to a light source,such as a laser beam that is recording data pages to the holographicrecording medium. The photoactive monomer may be any monomer or monomerscapable of undergoing photoinitiated polymerization, and which, incombination with a binder component, meets the compatibilityrequirements of the present invention. Suitable photoactive monomersinclude those which polymerize by a free-radical reaction, e.g.,molecules containing ethylenic unsaturation such as acrylates,methacrylates, acrylamides, methacrylamides, styrene, substitutedstyrenes, vinyl naphthalene, substituted vinyl naphthalenes, and othervinyl derivatives. Free-radical copolymerizable pair systems such asvinyl ether mixed with maleate and thiol, vinyl ether functionalities,mixed with olefin are also suitable. It is also possible to usecationically polymerizable systems; a few examples are vinyl ethers,alkenyl ethers, allene ethers, ketene acetals, epoxides, etc.Furthermore, anionic polymerizable systems are suitable. It is alsopossible for a single photoactive monomer molecule to contain more thanone polymerizable functional group. Other suitable photoactive monomersinclude cyclic disulfides and cyclic esters. Oligomers that may beincluded in the polymerizable component to form a grating upon exposureto a light source include oligomers such as oligomeric (ethylenesulfide) dithiol, oligomeric (phenylene sulfide) dithiol, oligomeric(bisphenol A), oligomeric (bisphenol A) diacrylate, oligomericpolyethylene with pendent vinyl ether groups, etc.

In addition to the photoactive monomer, an article of the presentinvention may contain a photoinitiator. The photoinitiator, uponexposure to relatively low levels of the recording light, chemicallyinitiates the polymerization of the monomer, avoiding the need fordirect light-induced polymerization of the monomer. The photoinitiatorgenerally should offer a source of species that initiate polymerizationof the particular photoactive monomer. Typically, 0.1 to 20 vol %photoinitiator provides desirable results.

The monomers and/or oligomers of the polymerizable component of anarticle of the present invention may be monofunctional, difunctional,and/or multifunctional.

A variety of photoinitiators known to those skilled in the art andavailable commercially are suitable for use in the invention. It isadvantageous to use a photoinitiator that is sensitive to light atwavelengths available from conventional laser sources, e.g., the blueand green lines of Ar⁺ (458, 488, 514 nm) and He—Cd lasers (442 nm), thegreen line of frequency doubled YAG lasers (532 nm), and the red linesof He—Ne (633 nm), Kr⁺ lasers (647 and 676 nm), and various diode lasers(290 nm to 900 nm). One advantageous free radical photoinitiator isbis(η-5-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium,available commercially from Ciba as Irgacure 784™. Another visiblefree-radical photoinitiator (which requires a co-initiator) is5,7,diiodo-3-butoxy-6-fluorone, commercially available from SpectraGroup Limited as H-Nu 470. Free-radical photoinitiators of dye-hydrogendonor systems are also possible. Examples of suitable dyes includeeosin, rose bengal, erythrosine, and methylene blue, and suitablehydrogen donors include tertiary amines such as n-methyl diethanolamine. In the case of cationically polymerizable monomers, a cationicphotoinitiator is used, such as a sulfonium salt or an iodonium salt.These cationic photoinitiator salts absorb predominantly in the UVportion of the spectrum, and are therefore typically sensitized with asensitizer or dye to allow use of the visible portion of the spectrum.An example of an alternative visible cationic photoinitiator is(η₅-2,4-cyclopentadien-1-yl) (η₆-isopropylbenzene)-iron(II)hexafluorophosphate, available commercially from Ciba as Irgacure 261.

In most embodiments, photoinitiators of the present invention aresensitive to ultraviolet and visible radiation from 200 nm to 800 nm.

An article of the present invention may also include additives such asplasticizers for altering the properties of the article of the presentinvention including the melting point, flexibility, toughness,diffusibility of the monomers, and ease of processibililty. Examples ofsuitable plasticizers include dibutyl phthalate, dichlorohexane,N,N-dimethylformamide, etc. Plasticizers differ from solvents in thatsolvents are typically evaporated whereas plasticizers are meant toremain in the article.

Some articles of the present invention may include plasticizers that actas slow thermosetting agents that thermoset a thermoplastic in theholographic recording medium by becoming crosslinked with thethermoplastic over a period of time once the holographic recordingmedium has been processed in a liquid state and allowed to cool. Forexample, when poly(methyl vinyl ether-alt-anhydride) is used as athermoplastic in the binder component, glycerol ethoxylate may be usedas a slow thermosetting agent, because the anhydride units in thethermoplastic may eventually react with the hydroxyl moieties in theslow thermosetting agent, but this reaction may not be significantduring the process of forming the article, allowing the article tobehave primarily as a thermoplastic with respect to melting, flowing andthen solidifying over a short time scale. Any pair of functionalitiesthat are slow to thermally react may be used to devise a suitable slowthermosetting system. For example, alcohols and epoxides are typicallyvery slow to react (without a catalyst or with a poor catalyst) andthus, one may use a polyol binder with a multifunctional epoxide as theslow thermosetting agent. Other such pairings include, slow Diels-Alderreactions, hindered alcohols with hindered isocyanates, epoxides withcyclic anhydrides, etc.

Other types of additives that may be used in the liquid mixture andarticle of the present invention are inert diffusing agents havingrelatively high or low refractive indices. Other additives that may beused in the liquid mixture and article of the present invention include:pigments, fillers, nonphotoinitiating dyes, antioxidants, inhibitors,bleaching agents, mold releasing agents, antifoaming agents,infrared/microwave absorbers, surfactants, etc.

It has been determined that use of a thermoplastic binder and less than20 volume % photoactive monomer/oligomer gives a medium capable ofholographic recording; however, other formulations of thermoplasticbinders and photoactive monomers/oligomers may also be used in thepresent invention. Such a medium has a melting temperature above roomtemperature (preferably at least 10° C. above room temperature), andthus is a solid at room temperature. Fabrication of optically flatarticles typically requires heating of the mixture used to make anoptically flat medium above the softening or melting temperature of themedium. Once flatness is obtained, the medium is allowed to cool andthus return to solid thereby keeping the flatness of the medium. Uponexposure to light of appropriate wavelength for the photoactivemonomer/oligomers (which includes multiple types of monomers as well aspossibly mono, di, and multifunctional monomers/oligomers), the articlemay record the spatial light pattern, thus forming a hologram.

Although in one embodiment, the polymerizable component, consisting ofone or more photoactive monomers and possibly one or more oligomers, ofan article of the present invention is less than 20 volume %, in otherembodiments, the polymerizable component of an article of the presentinvention may be less than 10 volume %, or even less than 5 volume %.

An article of the present invention may be any thickness needed. Forexample the article may be thin for display holography or thick for datastorage. The article may be a film deposited on a substrate, a freeflexible film (similar to food wraps) or a hard article requiring nosubstrate (similar to a credit card).

An article of the present invention may be heated to form a liquidmixture that is infused into a porous substrate such as glass (Vycor™),cloth and paper, wood or plastic; then allowed to cool. Such articleswould be able to record holograms of a display and/or data nature.

An article of the present invention may be made optically flat via theappropriate processes, such as the process described in U.S. Pat. No.5,932,045, the entire contents and disclosure of which is herebyincorporated by reference.

Also, the ability to use a wider variety of thermoplastics in an articleof the present invention allows for the possible reduction orelimination of problems such as water or humidity that affect currentholographic storage media. In one embodiment, the article of the presentinvention may be used to store volatile holograms. Due to thethermoplastic nature of the present invention, a particular mixture maybe tuned to have a very general lifetime for the recorded holograms.Thus, after hologram recording, the holograms may be readable for adefined time period such as a week, a few months, or years. Over time,the article may be allowed to slowly creep, and thus destroy thereadability of the holograms. Heating the article may also increase sucha process of hologram destruction. Examples of applications for usingvolatile holograms include: rental movies, security information, tickets(or season passes), thermal history detector, time stamp, and/ortemporary personal records, etc.

In one embodiment, an article of the present invention may be used torecord permanent holograms. In such an embodiment, the T_(g) of thearticle either increases or the mixture crosslinks during hologramformation. In the former case, the dissolved polymerizable component(behaving as a plasticizer) substantially lowers the melting temperatureof the binder component, yet when a hologram is written, the monomer isessentially depleted and thus the plasticization effect is eliminated,thereby increasing the melting temperature of the post-recordedmaterial. In the latter case, the binder may be telechelic ormultifunctional with a polymerizable functionality capable of reactingwith the monomer that allows for crosslinking during hologram formation.Alternatively, the binder component may have a slow thermosetting agentas described previously.

In one embodiment of the present invention, photobinding of photoactivemolecules to the binder occurs. Suitable photoactive molecules for thisapplication include: thiols, selenols, tellenols, disulfides,diselenides, ditellurides, and various photoiniferters. Additionally,molecules that are known to be both monomers and photoinitiators such asmaleimides and maleic anhydrides are suitable photoactive molecules.Also suitable as photoactive molecules for photobinding are free radicalphotoinitiators (whether they be cleavage, hydrogen abstraction,electron transfer-proton transfer, or a combination of the three). Thesephotobinding reactions typically would use a binder with unsaturateddouble bonds as the photobinding receptor. However, if a photobase or aphotoacid generator were the photoactive molecule, then a binder withacid functionality or base functionality as photobinding receptors,respectively, may be used. In such an embodiment, it is understood thatone could have an oligomer with photobinding receptors as well asfunctionality that allows for either covalent or noncovalent bonding tothe binder or several other very similarly related configurations.

In one embodiment of the present invention, an article of the presentinvention may be used to store reversible holograms. Suitablephotoactive molecules of the photoactive component include moleculescontaining C—C double bonds that undergo any of the various types ofreversible photocycloaddition reactions. These may include anthracenes,acenaphthylenes, phenanthrenes, and related polyaromatic hydrocarbons,photodiene formation/Diels Alder reactions, and concerted andnonconcerted ene-ene reactions (2+2, 4+4, 4+2, 3+2, etc.). Also, metaland organic salts may be attached to photochelating groups, such asspiro compounds, chromenes, and the like. Nucleotides, such as DNA andRNA, may also be attached to such compounds via strong hydrogen bondinginteractions. Polymer-bound metal complexes may be used as attachmentsites for photoinsertion of various ligands. This list is exemplary andmodifications or additions to the list may be determined by one ofordinary skill in the art in light of the teachings of the presentinvention.

Preferably, the photoactive molecules of the photoactive component reactduring hologram formation by a cycloaddition reaction. There are avariety of cycloaddition reactions that yield rings of different sizes,and that may be reversed using light of shorter wavelength than thewavelength first used to react the components, or using heat.Four-member rings (cyclobutanes) may be formed by (2+2) cycloadditions,and 8-membered rings may be formed by (4+4) cycloadditions.Acenaphthylenes, which are an example of species that undergo (2+2)cycloaddition reactions, are a more preferred type of write component.Acenaphthylenes typically posses a high refractive index and undergoforward and reverse reactions with a high quantum efficiency and minimalside reactions. Further, the forward and reverse photoreactions are atwavelengths that are easily accessible with current laser and lightsources. Preferably, the binding of the photoactive molecules of thephotoactive component to the binder may be reversed by exposing theoptical article to light of a different wavelength than was used to bindthe photoactive molecules of the photoactive component to the binder.Preferable binders for use with acenaphtylene-derived photoactivemolecules are thermoplastic resins with pendent photobinding receptorsof vinyl ether functionality. Suitable materials, includingphotoreversible photoactive molecules, for use in such articles aredescribed in U.S. patent application Ser. No. 10/411,380, filed Apr. 11,2003, the entire contents and disclosure of which is hereby incorporatedby reference.

An article of the present invention may be ground, shredded, fragmented,etc. to form a particle material of powder, chips, etc. The particlematerial may be heated at a later time to form a flowable liquid used tomake a molded product, a coating to apply to a substrate, etc.

When the particle material is a powder, the powder may beelectrostatically applied to a substrate such as metal and otherconductive materials (typical powder coating), which would then beheated to form a coating. The powder may also be infused into fibrousmaterials to form holographic paper, cardboard, ribbons, etc. fordecorative applications. Additionally, the powder may be melt extrudedinto a fiber for thread, yarn, and fabric applications.

An article of the present invention may be used in a variety of productsto provide tracking information. For example, the article may be part ofa cardboard shipping box, a sheet of material from which the shippingbox is made, or the paper in which a box is wrapped for shipping,package labeling, etc. The article may also be used for securitypurposes such as: a security label, part of a security label, a securitytag, a piece of clothing, etc. The article may be used in indoor oroutdoor advertising. For example, the article may be used in makingbillboards, park benches, as an advertising wrap for a vehicle, as asign for mounting in or on a bus or subway, as a sign in a subwaystation, etc.

An article of the present invention may also be used for decorativepurposes. For example, the article may be used in gift wrap or in windowtreatments to provide special artistic tinting or 3D designs. Thearticle may be ground-up and used in coatings such as paint for houses,automobiles, furniture, etc. The article may be used in molded parts ofautomobiles, toys, furniture, appliances, etc. to provide decorativeeffects.

An article of the present invention may also be used to make datastorage devices of various sizes and shapes, as a block of material oras part of a coating that is coated on a substrate.

EXAMPLES Example 1

A mixture was formed having the following composition:

-   -   3.0 g—Poly(methyl vinyl ether-alt-maleic anhydride)—Mn aprox        80,000    -   0.0103 g—Thionin Perchlorate    -   0.077 g—Tetraphenyl Borate salt (tetrabutyl amine cation)    -   0.1123 g—Tribromophenyl Acrylate    -   0.587 g—Glycerol Ethoxylate—Mn 1000    -   10 ml acetone

The mixture was mixed until homogenous and then acetone was evaporatedoff under reduced pressure and then heated to 60° C. for 5 minutes tolet bubbles escape. The remaining liquid mixture was then placed betweenheated glass substrates (glass temp was 80° C.) containing a Teflon™spacer of 250 microns. The mixture was then allowed to cool to form anarticle of the present invention.

Using a 635 nm diode laser to record data pages to this article, thisarticle produced a 4% diffraction grating. The grating was destroyed byheating to 60° C. for 20 minutes and upon heating to 100° C., the mediumwas able to flow, demonstrating that the medium was still athermoplastic.

Example 2

A mixture was formed having the following composition:

-   -   2.086 g—Poly(Vinyl Acetate)—Mw 83,000    -   0.189 g—Bisphenol A Glycerolate (1 glycerol/phenol) diacrylate    -   0.127 g—Hydroxypropyl Acrylate    -   0.101 g—Glycerol Propoxylate—Mn 1500    -   0.01 g—Darocure™ TPO (obtained from Ciba-Geigy)

The mixture was heated to 60° C. for 8 hours, then, while still hot,placed between 2 heated glass substrates. A thickness of 200 microns wasobtained and the mixture was allowed to cool to room temperature,whereupon a homogenous, clear, bubble free article of the presentinvention was produced. Using a 407 nm diode laser to holographicallyrecord pages of data to this article, this article gave a shrinkageunder 0.5% and a M/# for a 200 micron thick material of 2.75.

Example 3

An article using a telechelic binder is formed having the followingcomposition:

-   -   90 wt % Poly(vinyl acetate-co-alcohol) with pendant vinyl ether    -   5 wt % Writing monomer such as a difunctional acrylate of        Bisphenol A    -   0.2 wt % Darocure™ TPO (blue light sensitive initiator)    -   0.1 wt % Irganox™ Brand Antioxidant    -   4.7 wt % Inert plasticizer such as poly(ethylene oxide) Mn=2000

This article may be formed using a process similar to that describedabove in Example 1 or 2. Alternatively, the composition may be processedin a standard thermoplastic manner such as placing all components into ahopper for grinding and mixing, and then extruding the resultantthermoplastic into a desired shape. This formulation is a thermoplasticuntil recording of the hologram, then the acrylate copolymerizes withthe binder (via the vinyl ether linkages) to ultimately thermoset themixture.

Example 4

An article providing an elevated T_(g) and melting temperature is formedhaving the following composition:

-   -   95 wt % Poly(vinyl acetate-co-alcohol) with pendant vinyl ether        (attached by reaction to the alcohol)    -   4.6 wt % Writing monomer such as a difunctional acrylate of        Bisphenol A ethoxylate    -   0.2 wt % Darocure™ TPO (blue light sensitive initiator)    -   0.1 wt % Irganox™ Brand Antioxidant

This article may be formed using a process similar to that describedabove in Example 1 or 2. Alternatively, the composition may be processedin a standard thermoplastic manner such as placing all components into ahopper for grinding and mixing, and then extruding the resultantthermoplastic into a desired shape. During recording, this articleincreases in both T_(g) and melting temperature since the presence ofthe writing component effectively behaves as a plasticizer until it ispolymerized during the recording of a hologram.

Example 5

An article employing non-covalent crosslinking is formed having thefollowing composition:

-   -   95 wt % Poly(maleic anhydride-co-butyl vinyl ether) with some of        the anhydride groups' ring opened to form an alkyl ester and a        carboxylic acid    -   0.1 wt % Tertiary Amine Acrylate (such as 2-(diethylamino) ethyl        acrylate)    -   4.1 wt % A polymerizable component such as a monofunctional        acrylate (tribromophenyl acrylate)    -   0.1 wt % A surfactant additive (the surfactant will ensure that        the ionic centers do not phase separate into domains large        enough to scatter light).    -   0.2 wt % A photoinitiator component

This article may be formed using a process similar to that describedabove in Example 1 or 2. Alternatively, the composition may be processedin a standard thermoplastic manner such as placing all components into ahopper for grinding and mixing, and then extruding the resultantthermoplastic into a desired shape or between two transparentsubstrates. An important part of this formulation is using the same molepercent aminoacrylate as carboxylic acid. These two components form asalt complex. The salt complex forms ionic centers that have a weakerinteraction (intramolecular association) than the carboxylic acids wouldhave had by themselves (intermolecular association), thus the aminoacrylate breaks up the hydrogen bonding allowing for easier processingof the thermoplastic.

Recording holograms in this formulation causes the aminoacrylate and thepolymerizable component to copolymerize. Even though a linear polymer isformed, the linear polymer likely contains several amino acrylategroups, each of which is ionically linked to the thermoplastic, thuscreating a series of ionic crosslinks, which raises the meltingtemperature and T_(g) of the mixture.

Example 6

An article having reversible chemistry is formed having the followingcomposition:

-   -   95 wt % Poly(vinyl acetate-co-alcohol) with pendant vinyl ether        (attached by reaction to the alcohol)    -   0.5 wt % Writing monomer such as a difunctional acrylate of        Bisphenol A ethoxylate    -   0.025 wt % Irgacure 819™ (blue light sensitive initiator)    -   0.225 wt % Additive (plasticizer or inert diffusing agent)    -   0.25 wt % 1-Cyanoacenaphthylene

This article may be formed using a process similar to that describedabove in Example 1 or 2. Upon exposure to blue wavelengths of 440 nm,the mixture is crosslinked. This first exposure may be used to write ahologram of the display or data type. Upon further exposure to 405 nm, asecond hologram that is erasable may be formed. This hologram may beerased by irradiating the article at Deep UV wavelengths. After theerase step, the article is capable of recording a new hologram using 405nm light.

Example 7

An article having reversible chemistry is formed having the followingcomposition:

95 wt % Poly(vinyl acetate-co-alcohol) with pendant vinyl ether(attached by reaction to the alcohol)

-   -   4.75 wt % Additive (plasticizer or inert diffusing agent)    -   0.25 wt % 1-Cyanoacenaphthylene

This article may be melt processed using extrusion into a solid articleof various thicknesses. The solid article is capable of rewriteable datastorage.

Example 8

An article using write-once chemistry for hologram formation is formedusing the following composition:

-   -   90 wt % Poly(vinyl acetate-co-alcohol) with pendant vinyl ether        (attached by reaction to the alcohol)    -   5 wt % Additive (plasticizer or inert diffusing agent)    -   5 wt % Photoinitiator (ex. Darocure™ TPO from Ciba-Geigy)

This article may be melt processed using extrusion into a solid articleof various thicknesses. The solid article is capable of displayholography with applications as a decorative coating.

Example 9

An article using only 5 wt % thermoplastic binder is formed using thefollowing composition:

-   -   5 wt % Poly(ethylene oxide) with 5% pendant vinyl ether        (attached by reaction to the alcohol)    -   80 wt % Additive (nanoparticulate fumed silica with dye absorbed        to the surface to impart both solubility and color)    -   10 wt % Plasticizer    -   5 wt % Photoinitiator (ex. Irgacure 784™)

This formulation may be heated and injected between two substrates. Thedye color may be any color that does not absorb green light appreciably.The solid article would be capable of display holography and wouldrepresent a temporary hologram since heating of the article afterrecording of the hologram will result in the destruction of thehologram.

All documents, patents, journal articles and other materials cited inthe present application are hereby incorporated by reference.

Although the present invention has been fully described in conjunctionwith several embodiments thereof with reference to the accompanyingdrawings, it is to be understood that various changes and modificationsmay be apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims, unless they departtherefrom.

1.-66. (canceled)
 67. A method for making a solid article comprising thefollowing steps: (a) mixing together a binder component, a polymerizablecomponent and a photoinitiator component to form a mixture; (b) heatingsaid mixture to form a substantially homogeneous liquid; and (c) coolingsaid liquid to form said solid article, wherein said binder componentcomprises at least one thermoplastic, wherein said polymerizablecomponent comprises at least one photoactive monomer that is soluble insaid binder component, wherein said photoinitiator component comprisesat least one photoinitiator that causes said polymerizable component toform a polymer or co-polymer when a portion of said polymerizablecomponent is exposed to a light source, and wherein said article iscapable of recording spatial light distribution via a spatial refractiveindex change.
 68. The method of claim 67, wherein said article isvolatile compound free.
 69. The method of claim 67, wherein said articlehas a melting point at least 10° C. greater than room temperature. 70.The method of claim 67, further comprising the following steps: (d)heating said article to form a flowable material; and (e) forming saidflowable material into a product having a different form than saidarticle.
 71. The method of claim 70, wherein step (e) comprises moldingsaid flowable material to form a molded product.
 72. The method of claim70, wherein step (e) comprises forming said flowable material into afree flexible film.
 73. The method of claim 70, wherein step (e)comprises depositing said flowable material as a film on a substrate.74. The method of claim 70, wherein step (e) comprises extruding saidflowable material as an extruded product.
 75. The method of claim 70,wherein step (e) comprises forming said flowable material into a sheetof material.
 76. The method of claim 70, wherein step (e) comprisesforming said flowable material into a stiff sheet.
 77. The method ofclaim 70, wherein step (e) comprises infusing said flowable materialinto a porous substrate to form a composite product.
 78. The method ofclaim 77, wherein said porous substrate comprises glass.
 79. The methodof claim 77, wherein said porous substrate comprises paper.
 80. Themethod of claim 77, wherein said porous substrate comprises plastic. 81.The method of claim 77, wherein said porous substrate comprises cloth.82. The method of claim 67, further comprising the following steps: (d)sub-dividing said article to form a particle material.
 83. The method ofclaim 82, further comprising the following steps: (e) heating saidparticle material to form a flowable material; and (f) forming saidflowable material into a product.
 84. The method of claim 82, whereinsaid particle material comprises a powder.
 85. The method of claim 82,wherein said particle material comprises a plurality of chips.
 86. Themethod of claim 82, further comprising coating a substrate with saidparticle material to form a coated product.
 87. The method of claim 67,further comprising molding said liquid mixture to form a molded productcomprising said article.
 88. The method of claim 67, further comprisingforming said liquid mixture into a free flexible film comprising saidarticle.
 89. The method of claim 67, further comprising depositing saidliquid mixture as a film on a substrate, wherein said film comprisessaid article.
 90. The method of claim 67, further comprising extrudingsaid liquid mixture to form an extruded product, wherein said extrudedproduct comprises said article.
 91. The method of claim 67, furthercomprising forming said liquid mixture into a sheet of materialcomprising said article.
 92. The method of claim 67, further comprisingforming said liquid material into a stiff sheet comprising said article.93. The method of claim 67, further comprising infusing said liquidmixture into a porous substrate to form a composite product comprisingsaid article.
 94. The method of claim 93, wherein said porous substratecomprises glass.
 95. The method of claim 93, wherein said poroussubstrate comprises paper.
 96. The method of claim 93, wherein saidporous substrate comprises plastic.
 97. The method of claim 93, whereinsaid porous substrate comprises cloth.
 98. The method of claim 67,wherein said article is substantially optically flat.
 99. The method ofclaim 67, wherein said liquid is deposited between two substrates. 100.The method of claim 99, wherein said substrates have antireflectivecoatings coated thereon and wherein said article is substantiallyoptically flat.
 101. A method for holographically recording a spatiallight distribution via a spatial refractive index change to aholographic recording medium comprising: providing said holographicrecording medium; and forming holographic gratings in said holographicrecording medium by holographically recording said spatial lightdistribution via said spatial refractive index change to saidholographic recording medium, wherein said holographic recording mediumcomprises: a binder component comprising at least one thermoplastic; apolymerizable component comprising at least one photoactive monomer thatis soluble in said binder component; and a photoinitiator componentcomprising at least one photoinitiator that causes said polymerizablecomponent to form a polymer or co-polymer when a portion of saidpolymerizable component is exposed to a light source.
 102. A system forholographically recording a spatial light distribution via a spatialrefractive index change to a holographic recording medium comprising:said holographic recording medium; and means for forming holographicgratings in said holographic recording medium by recording said spatiallight distribution via said spatial refractive index change to saidholographic recording medium, wherein said holographic recording mediumcomprises: a binder component comprising at least one thermoplastic; apolymerizable component comprising at least one photoactive monomer thatis soluble in said binder component; and a photoinitiator componentcomprising at least one photoinitiator that causes said polymerizablecomponent to form a polymer or co-polymer when a portion of saidpolymerizable component is exposed to a light source. 103.-106.(canceled)
 107. A method for making a solid article comprising thefollowing steps: (a) mixing a binder component with a photoactivecomponent; (b) heating said mixture to form a substantially homogeneousliquid; and (c) cooling said liquid to form said solid article, whereinsaid binder component comprises at least one thermoplastic, wherein saidphotoactive component comprises at least one photoactive molecule, andwherein said solid article is capable of recording spatial lightdistribution via a spatial refractive index change.
 108. The method ofclaim 107, wherein said spatial refractive index change is causedprimarily by mass diffusion and wherein said article has a melting pointat least 10° C. greater than room temperature.
 109. The method of claim107, wherein said photoactive component is photoreversible and whereinsaid binder component contains photobinding receptors.
 110. A method forholographically recording a spatial light distribution via a spatialrefractive index change to a holographic recording medium comprising thefollowing steps: (a) providing said holographic recording medium; and(b) forming holographic gratings in the holographic recording medium byholographically recording said spatial light distribution via saidspatial refractive index change to said holographic recording medium,wherein said holographic recording medium comprises: a binder componentcomprising at least one thermoplastic; and a photoactive componentcomprising at least one photoactive molecule.
 111. The method of claim110, wherein said spatial refractive index change is caused primarily bymass diffusion, and wherein said article has a melting point at least10° C. greater than room temperature.
 112. A system for holographicallyrecording a spatial light distribution via a spatial refractive indexchange to a holographic recording medium comprising: (a) saidholographic recording medium; and (b) means for forming holographicgratings in said holographic recording medium by recording the spatiallight distribution via said spatial refractive index change to saidholographic recording medium, wherein said holographic recording mediumcomprises: a binder component comprising at least one thermoplastic; anda photoactive component comprising at least one photoactive molecule.113. The system of claim 112, wherein said spatial refractive indexchange is caused primarily by mass diffusion and, wherein said articlehas a melting point at least 10° C. greater than room temperature.